Assays for detecting the presence and level of a variety of analytes in body fluid samples are known. Such assays are often designed for simplicity of use so that they can be reliably conducted in a doctor's office or other clinical setting where personnel may have little training in clinical assay procedure or in interpreting assay results. In order to minimize the need for operator involvement, it is preferable that the assay be carried out in an automated or self-contained manner.
Such self-contained assays have typically been limited, for the sake of simplicity of operation, to one-step assay procedures. A number of useful assays, however, are multistage in nature, requiring more than one reacting or binding step. Further, one or more of the steps may be rate limiting, or the rate of liquid flow from one assay region to another may be dependent on the nature of the sample. Typically, multistage assays are less readily automated and generally require more input from the user, thus increasing the possibility of error.
It is therefore desirable to provide an automated, self-contained assay device which is able to perform multistage assays, in particular those containing multiple reacting or binding steps in which rates of sample movement within an assay device, or rates of assay reactions are variable, depending on the nature of the sample and the assay being performed.